Concentrations of metabolic lead in buried ancient bones are obscured by replacement of calcium n apatite by excessive amounts of soil moisture Pb. Concentrations of metabolic barium in bones are affected in a similar way. Added soil Pb and Ba, expressed as log(Pb/Ca) vs log(Ba/Ca) among various bones at a given burial site, are positively covariant, with about 5-fold more soil Pb added for each unit of added soil Ba. The typical natural metabolic Ba/Ca ratio in contemporary people can be measured unambiguously because it is unaffected by industrial pollution. It applies to ancient people because it has not changed historically. The intercept of the covariance curve for buried bones of a given ancient population at the known metabolic Ba/Ca ratio indexes the corresponding metabolic Pb/Ca ratio in bones of that population. Pb levels which prevailed in Romans are similar to those in contemporary people, and both are 1000-fold above natural levels determined by this method in ancient Peruvians. The proposed study is designed to measure the pre-Industrial baseline levels of lead in two prehistoric American populations. Lead, calcium, and barium will be measured in teeth, femurs and ribs of 2 groups of 20 prehistoric Chumash of Malibu, CA and Anasazi of Rainbow Bridge, AZ using isotopic dilution mass spectroscopy. We will determine the baseline concentrations, estimate population variances and the degree of soil moisture contamination on each of the three bony tissues. Age and gender identification of these people will allow us to study the degree of bioaccumulation of lead with age which is observed for modern populations. Finally, we will examine whether males bioaccumulate more lead than females, which is observed in modern populations, in order to suggest whether these observed modern differences are the result of differential exposure to environmental lead or other mechanisms. The results will be useful in future policy decisions regarding international standards for lead in gasoline.